The present invention relates to a pivot assembly for connecting a cover member to a housing of a sliding closure unit employed for controlling the discharge of molten metal from a metallurgical vessel and of the type including a housing fixed to the metallurgical vessel, at least one stationary refractory plate positioned within the housing, a movable refractory plate mounted within the housing for movement relative to the stationary refractory plate, a cover member for pressing together the refractory plates to urge respective abutting sliding surfaces thereof into sealing contact, and a pivot shaft pivotally connecting the cover member to the housing so that the sliding closure unit may be opened for replacement of the refractory plates.
In this type of sliding closure unit, there must be provided play in the pivot assembly to ensure that, in the operating position of the sliding closure unit, the movable plate will be pressed, free from tilting or binding, against the bottom stationary refractory plate, or in the case of a three-plate sliding closure unit, against the stationary bottom plate and the stationary stay plate. That is, it is necessary during operation of the sliding closure unit that the sliding surfaces of the refractory plates are free of binding and are maintained in substantially uniform surface-to-surface contact under the influence of the pressure exerted by the cover member.
West German DE-OS No. 21 61 368 discloses an arrangement whereby play is provided by the cover member having therethrough a hole or opening which fits over a pivot shaft supported by the housing, the hole or opening having a larger diameter than the diameter of the shaft. Thus, play is provided to enable the cover member, and thereby the refractory plates supported thereby, to accommodate forces such as expansion, etc., during operation to ensure that the sliding surfaces of the refractory plates are free of binding and are maintained in substantially uniform surface-to-surface contact while being pressed together by the cover member. However, this arrangement is effective only up to a certain point, since during movement of the movable refractory plate, during which time friction is generated between the abutting sliding surfaces, the loose pivot assembly enables displacement of the cover member relative to the housing. To prevent this disadvantage, the above known arrangement provides abutment surfaces extending transverse to the direction of movement of the movable refractory plate to thereby prevent displacement of the cover member relative to the housing and to guide the pressing movement of the cover member toward the refractory plates.
West German DE-OS No. 24 59 568 discloses another arrangement wherein the pivot shaft of the assembly is mounted on the cover member and guided in slots provided in the housing and extending in the direction in which the refractory plates are pressed, or perpendicularly to the respective sliding surfaces thereof. These slots thereby provide free play to the cover member to uniformly urge the refractory plates against one another. A disadvantage of this known arrangement however is the relatively elaborate fabrication of the slots compared to a single hole or opening. Furthermore, in an arrangement whereby the pivot assembly extends transverse to the direction of movement of the movable refractory plate, the pivot shaft can be pressed onto the guiding surfaces of the slots due to the frictional forces generated during movement of the movable refractory plate, thereby eliminating the play of the cover member.